The invention relates to a rain water filter having a housing, which is provided with a horizontally running lateral inlet, a horizontally running lateral residual water outlet for unfiltered water and a filter water outlet for filtered water, wherein a horizontally running upper water course connects to the inlet in the housing, which leads to the residual water outlet, and having a filter for filtering the inflowing water, the filter surface of which follows the upper water course in the horizontal direction.
This type of rain water filter is described in DE 199 42 240 C2. The inlet and the residual water outlet lie at the same height in relation to the installation position of the rain water filter. They are connected to each other via a horizontally running filter pipe, which forms the upper water course. It extends over the filter water outlet. The water flows via the inlet into the one end of the filter pipe, wherein a portion of the water penetrates through the meshes of the filter pipe through the force of gravity and flows to the filter water outlet, while the other portion passes through the filter pipe and reaches the residual water outlet.
Because the inlet and the residual water outlet are at the same height, the height of the housing is relatively small. As a result, it can also be installed readily in an entrance hole of a cistern.
However, the disadvantage of this arrangement is that, particularly when the water flow is low, residues that are filtered out are left behind in the filter pipe, which clogs the filter pipe little by little so that it must be cleaned regularly.
Therefore, the invention is based on the objective of creating a rain water filter, which has a low installation height and is self-cleaning despite a low offset between the inlet and the residual water outlet.
To attain this objective, the invention provides that the residual water outlet is downwardly offset in relation to the inlet, that a horizontally running lower water course is located below the upper water course, which merges into the residual water outlet and that the filter is arranged such that the unfiltered water running off from the inlet side of the filter reaches the lower water outlet and from there the residual water outlet.
With this type of filter, a vertical flow occurs along the substantially vertically aligned filter surface, which prevents filter residues from depositing there. Instead the filter residues are always flushed from the inlet side of filter through the support of gravity.
The filter is preferably an adhesive filter. The type of rain water filter, in which the water runs off on a substantially vertically aligned filter surface and is pulled through the filter in the process through the forces of adhesion, is known, for example, from DE 38 12136 A1. The filter is a so-called adhesive filter, which is designed as a pipe and is arranged vertically in the housing of the rain water filter. The inflowing water runs vertically into the pipe and through the pipe into a residual water outlet located below the pipe, which is arranged on the base of the rain water filter housing. The water suctioned through the adhesive filter reaches a collection chamber on the lower end of an annular space between the pipe and the housing and is routed from there into a cistern via a lateral filter water outlet.
In order to obtain an adequate yield, the filter pipe requires a certain height so that the distance between the inlet on the upper end of the pipe and the filter water outlet on the lower end of the pipe is relatively large, which makes this type of rain water filter unsuitable to be accommodated in the entrance hole of a cistern.
Because, according to the invention, the vertical height of the filter cannot be very large (the offset between the inlet and the residual water outlet is supposed to remain low), a certain length of the filter is required. This is achieved in that the upper water course is formed by a channel, which has a longitudinal slot on its base, wherein the filter is located below the longitudinal slot.
The water consequently flows from the inlet via the upper water course in the direction of the filter water outlet, wherein, on its path along the upper water course, the water runs downwardly through the longitudinal slot and encounters the filter there. There it runs vertically along the filter surface and is suctioned in part through the filter, while the non-suctioned portion reaches the other water outlet and from there also the residual water outlet.
So that the water flows into the longitudinal slot in a manner that is distributed as equally as possible over the length of the longitudinal slot, it is provided that the size of the local curvature of the base of the channel in the region of the longitudinal slot gets smaller from the inlet end towards the residual water outlet end.
The channel is thus flatter on the inlet end than on the residual water outlet end. Because the water quantity on the inlet end is still large and the water level therefore has a certain height above the channel base, the water is already pushed by its pressure in the direction of the longitudinal slot so that the base regions on both sides of the longitudinal slot do not require a large transverse gradient (inclination in the direction of the longitudinal slot). The water quantity has already gotten smaller on the residual water outlet end, which, however, is compensated for by an enlarged transverse slope.
The shape of the channel base can be an ellipse, a cycloid or preferably a clothoid, wherein the parameters thereof change towards the residual water outlet end such that a circle is present there.
Two filter surfaces are provided to increase the yield. To this end, the filter consists of a half shell with a U-shaped cross-section, wherein the half shell sits with its open side downward on the lower water course and the crown of the half shell runs below the longitudinal slot. The filter surfaces are located in both walls of the half shell.
The water flowing through the longitudinal slot therefore encounters the crown of the half shell and flows further downward on both sides of the half shell, along the filter surfaces. In the process, the largest portion of the water reaches the interior of the half shell through the filter based on an adhesion effect, wherein a filtering takes places.
So that the filtered water can reach a filter water outlet, there is a longitudinal opening in the lower water course between the lateral walls of the half shell; in addition, a tank is located below the lower water course, which tank is connected to the filter water outlet.
Thus, the filtered water flows through the longitudinal opening into the tank and from there further into the filter water outlet. In the process, the tank acts as buffer for cases when more filtered water accrues than is able to flow off directly into the filter water outlet.
To prevent unfiltered water from getting under the half shell, the half shell is closed on the ends thereof.
In one concrete embodiment, the housing of the rain water filter has two opposing end walls, wherein the inlet is located in the one end wall and the residual water outlet is located in the other end wall. A hollow cylinder that is open on both sides and merges with a uniform cross-section into the residual water outlet runs between the end walls. Located in the upper portion of the hollow cylinder is a pipe, which connects with a uniform cross-section to the inlet. Because the pipe has a smaller cross-section than the hollow cylinder, a crescent space forms between the outer wall of the pipe and the inner wall of the hollow cylinder. It serves to accommodate the filter. The pipe therefore forms an upper water course, while the hollow cylinder forms the lower water outlet.
The end walls are preferably connected to each other via a half-shell-shaped base, which forms the tank to receive the filtered water, wherein the longitudinal edges of the base lie against the outer sides of the hollow cylinder in order to form a closed receiving space.
Even though this type of filter does not tend to get clogged up, a cleaning is in fact required from time to time. Therefore, the invention provides for the hollow cylinder to be held detachably on the end walls. As a result, the hollow cylinder can be removed from the housing for cleaning.
For this purpose, it is provided that a half-arc runs on the inner side of the one end wall, into which the one end of the hollow cylinder can be inserted from above and a collar or an offset for the uniform cross-sectional accommodation of the pipe is formed on the inner side of the other end wall.
The invention will be explained in greater detail in the following on the basis of one exemplary embodiment.